Method and apparatus for preform consistency

ABSTRACT

According to one embodiment of the present invention a method of creating a composite with an object having a central axis is provided which comprises wrapping a first fabric layer around the object in one of a clockwise or a counterclockwise direction around the central axis of the object. A second fabric layer is wrapped over the first fabric layer. The second fabric layer is wrapped around the object in the other of the clockwise or the counterclockwise direction around the central axis. The object is placed in a mold and resin is injected into the mold to form the composite.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/063,156filed Feb. 22, 2005, entitled Method and Apparatus for PreformConsistency.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of composites and, moreparticularly, to a method and apparatus for preform consistency.

BACKGROUND OF THE INVENTION

One technique utilized in the fabricating composites is resin transfermolding (RTM). RTM generally involves placing fiber or preformreinforcements between mold pieces and then injecting resin or moldbetween the mold pieces. Both the mold and resin may be heated asneeded, depending on the particular application. After the resin or moldhas cured, the mold may be opened to retrieve the generated composite,which comprises a combination of the fiber reinforcements and mold.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention a method ofcreating a composite with an object having a central axis is providedwhich comprises wrapping a first fabric layer around the object in oneof a clockwise or a counterclockwise direction around the central axisof the object. A second fabric layer is wrapped over the first fabriclayer. The second fabric layer is wrapped around the object in the otherof the clockwise or the counterclockwise direction around the centralaxis. The object is placed in a mold and resin is injected into the moldto form the composite.

Certain embodiments may provide a number of technical advantages. Forexample, a technical advantage of one embodiment may include thecapability to maintain radome fabric volume within a mold. Othertechnical advantages of other embodiments may include the capability toincrease the thickness of radome shell composites.

Although specific advantages have been enumerated above, variousembodiments may include all, some, or none of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the following figures,description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present invention andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIGS. 1 and 2 illustrate a clockwise wrapping of radome fabric around amolding object, according to an embodiment of the invention;

FIGS. 3 and 4 illustrate a counterclockwise wrapping of the radomefabric around the molding object, according to an embodiment of theinvention; and

FIG. 5 is a process flow diagram of an embodiment of a process ofwrapping a fabric around a molding object.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

It should be understood at the outset that although exampleimplementations of embodiments of the invention are illustrated below,the present invention may be implemented using any number of techniques,whether currently known or in existence. The present invention should inno way be limited to the example implementations, drawings, andtechniques illustrated below. Additionally, the drawings are notnecessarily drawn to scale.

In resin transfer molding (RTM), typical resins include, but are notlimited to, epoxy, vinyl ester, methyl methacrylate, polyester,phenolic, polymers of the preceding, arimid, carbon, synthetic fibers,other suitable resin materials, and combinations of the preceding. Theresin or mold may additionally include fillers such as alumnumtrihydratesm, calcium carbonate, and other suitable fillers. Typicalfiber reinforcements include, but are not limited to, glass, carbon,arimid, other suitable fiber reinforcement materials, or combinations ofthe preceding.

In environments where electromagnetic communication occur through thecomposites, the composites may be made of radome material. The terms“radome”, “radome material”, and variations thereof may generally referto any material that is at least partially transparent toelectromagnetic waves (e.g., radio waves, other communicative waves, orthe like). Such radome material in some embodiments may protect aparticular object from environmental elements. Thus, in someembodiments, radome materials may facilitate protection of an objectwhile at least partially allowing electromagnetic waves to passtherethrough.

In the creation of some radome composites, general concerns may involvethe volume of the fiber occupied by the fiber reinforcements between themold pieces. For example, it may generally be desirable (1) to ensurethat the fiber reinforcements can be placed into the final mold forresin transfer (e.g., between the molding pieces), and (2) to ensurethat the fiber reinforcements are placed in a manner that maintainsconsistent radiofrequency (RF) properties in the produced radomecomposite. These concerns are elevated when the produced radomecomposite are being utilized in a precession environment where RFperformance must be consistent throughout the various portions of theradome. As an example, some missiles with radome composite shellsrequire RF consistency not only around circumference, but also along thelength of the radome composite shell.

Techniques utilized in establishing a fiber volume include a variety ofwrapping techniques (e.g., for missile radome composite shells) such asa single direction pressure wind technique, a forced pressure intounwound layers technique, and a non-pressured layers technique. Each ofthese techniques, however, may result in inconsistent or uneven fibervolumes throughout the radome. For example, the single directionpressure wind technique tends to force the material into bunchescreating high-fiber volume locations resulting in poor RF properties forthe radome. The forced standard layers and non-pressurized techniqueslead to low-fiber volume areas in the tip region of the radome andhigh-fiber volume areas towards the base of the radome once the femalemold portion is added.

With these above concerns in mind, teachings of these invention aredirected towards a method that holds the fabric into place ensuring thatthe fiber volume remains in a desired location through RTM processing.With the fiber volume in the desired location, desired RF consistencymay be achieved after RTM.

FIGS. 1 and 2 generally illustrate a clockwise wrapping (e.g., in thedirection of arrow 60 around central axis 80) of radome fabric 50 arounda molding object 40 and FIGS. 3 and 4 generally illustrate acounterclockwise wrapping (e.g., in the direction of arrow 70 aroundcentral axis 80) of the radome fabric 50 around the molding object 40.FIG. 5 is a process flow diagram of an embodiment of a process 200 ofwrapping a fabric 50 around a molding object 40. With reference to FIGS.1-5, the following is an illustration of a process 200 of wrapping theradome fabric 50 around the molding object 40 in a manner that may allowfiber volume to remain in a desire location.

Referring to FIG. 1, object 40 may generally be any object in whichradome fabric 50 may be wrapped. In this particular embodiment theobject 40 is a male molding piece, utilized in producing a double curvedmissile shell radome composite. The male molding piece may complimentaryto a female molding piece (not explicitly shown). Once the male moldingpiece is completely wrapped, the male molding piece may be inserted intothe female molding piece and processed using RTM techniques.

Radome fabric 50 may be made of any suitable radome material operable tobe wrapped around the object 40. In this particular embodiment, theradome fabric 50 is an e-glass fabric. The radome fabric 50 may havevarying thicknesses and widths, depending on the particular application.In some embodiments the radome fabric 50 may have a thickness between1-50 mm and widths between a ¼ inch to ½ inch. In other embodiments,thickness may be less than 1 mm or greater than 50 mm and widths lessthan ¼ inch or greater than a ½ inch.

The radome fabric 50 may generally be wrapped around the object 40 withtension, compacting any lower layers of radome fabric 50 and drapefabric layers that may have been put into place. For example, as ageneral description of an embodiment, drape fabric layer(s) (notexplicitly show) may be placed on the male mode using conventional layupmethods. Then, to ensure that the drape fabric layers do not bulge,radome fabric 50 may be wound with tension, compacting the lower drapefabric layers. Then, more drape fabrics layer(s) may be laid followed byanother layer of radome fabric 50. Each wind of radome fabric 50 may bewound in the opposite direction of the last compression wound layer, forexample, in the direction of FIGS. 1 and 2 and then the in the directionof FIGS. 3 to 4.

Referring to FIG. 5, the process 200 may generally commence by setting acounter, N, equal to 0 (e.g., N=0) at step 210. The counter may then beincremented by one at step 220. The counter, as described in more detailbelow, may be utilized to determine which direction to wrap a layer ofradome fabric 50.

The process 200 may proceed to step 230 where a determination is made asto whether or not a drape fabric layer of fabric is needed. In someembodiments, such a drape fabric layer may not be needed while in otherembodiments such drape fabric layers may be needed. If a drape fabriclayer is needed, one or more drape fabric layers (not explicitly shown)may be placed on the object 40 at step 240. If a drape layer is notneeded, the process 200 may skip step 240 and proceed to step 250. Thedrape fabric layer may be substantially similar to the radome fabric 50,yet generally designed to drape over object. As an example of draping,three to five drape fabric layers may be placed on the object 40. Otherembodiments may include more or less drape fabric layers.

The process 200 may proceed (either skipping the drape process 240 orengaging in the drape process 240) to step 250 where a determination ismade as to the current state of the counter, N (e.g., even or odd). Ifthe counter is at an odd number, the process 200 may proceed to step 260where the radome fabric 50 is wrapped counterclockwise around the object40. If the counter is not at an odd number (e.g., the counter is an evennumber), the process 200 may proceed to step 260 where the radome fabricis wrapped clockwise around the object 40.

For purposes of illustration, the description of process 200 willproceed through step 260 (e.g., the counter, N, is not an odd number),coming back to step 270 on a subsequent loop. FIGS. 1 and 2 are anembodiment of step 260. FIG. 2 is a view taken along line 2-2 of FIG. 1.FIGS. 1 and 2 show a clockwise wrapping of the radome fabric 50 aroundobject 40—e.g., in direction of arrow 60 around a central axis 80 of theobject 40. The clockwise wrapping around the object 40 may either befrom a base 42 of the object 40 to a tip 44 of the object 40 or from thetip 44 of the object 40 to the base 42 of the object 40. The wrappingaround the object 40 is preferably a pressure wrapping or winding thatcompresses the underlying layers, ensuring that the radome fabric 50 andany underlying layers will maintain in desired position (e.g., a desiredvolume). Such compression may be accomplished by applying tension on theradome fabric during application of the radome fabric 50 on the object40.

The process 200 may proceed to step 280 where a determination is made asto whether or not the layers of fabric (e.g., drape fabric layers andradome fabric 50 combined) are the desired thickness. If so, the process200 may end. If not, the process 200 may loop back to step 220, wherethe counter, N, is incremented by one.

The process 200 on the subsequent loop may again determine whether ornot a drape layer needs to be established at step 230. If so, step 240will be processed again. If not, step 240 will be skipped.

At step 250, the decision process on this subsequent loop should makethe opposite decision made on the preceding loop because the counter wasincremented by one at step 220. Accordingly, the number should now beeven and the process 200 may proceed to step 270. FIGS. 3 and 4 are anembodiment of step 270. FIG. 4 is a view taken along line 4-4 of FIG. 3.FIGS. 3 and 4 show a counterclockwise wrapping of the radome fabric 50around object 40—e.g., in direction of arrow 70 around a central axis 80of the object 40. Similar to that described above, the counterclockwisewrapping around the object 40 may either be from the base 42 of theobject 40 to the tip 44 of the object 40 or from the tip 44 of theobject 40 to the base 42 of the object 40. Additionally, the wrappingaround the object 40 is preferably a pressure wrapping or winding thatcompresses the underlying layers, ensuring that the radome fabric 50 andany underlying layers will maintain in a desired position (e.g., adesired volume). Such compression may be accomplished by applyingtension on the radome fabric 50 during application of the radome fabric50 on the object 40.

The process 200, once again, proceeds to step 280 where a determinationis made as to whether or not the desired thickness has been achieved. Ifso, the process 200 ends. As an example of thickness, an embodiment mayutilize thirty three (33) total layers with the pressure wrapped radomefabric 50 being lay in a changing clockwise and counterclockwise fashionfor every three to five layers of drape layer placed on the object.

From the end of the process 200, the object 40 (male mold piece) havingthe radome fabric 50 and drape layers, if any, may be coupled to thefemale molding piece (e.g., placed inside the female molding piece) andthe RTM process may commence. The lay-up of the layers in the abovedescribed process 200 holds the fiber volume in place while the RTMprocess is utilized. With the fiber volume in place, consistent RFqualities may be achieved throughout the radome composite—for example,around the circumference and along the length of the radome (from tip tobase).

A variety of different RTM processes may be utilized, including, but notlimited to vacuum assisted resin transfer molding (VARTM). The moldmaterial may additionally be made a variety of organic and inorganicpolymers operable to serve as radome material. In some embodiments,processes other than RTM may be utilized.

Utilizing the above process, thicker missile radome composites may becreated than those using conventional techniques (e.g., techniquesproduced with ceramic materials). As an example, utilizing thistechnique a radome composite made of organic polymers may produce amissile shell almost ⅜ of an inch thick.

Although the above process has been generally been described wrapping inone direction and then wrapping in another direction, in otherembodiments of the invention, the wrapping may occur by wrapping twiceclockwise and twice counterclockwise. Additionally, the process maybegin by wrapping in either the clockwise or counterclockwise direction(e.g., start the increment, N, in process 200 of FIG. 5 at 1). Further,while the object 40 is generally shown in FIGS. 1-4 as a domed/conicalshaped object 40 in this embodiment, in other embodiments the object 40may take on a variety of other shapes, including but not limited tocolumnar, cubed, and the like.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present invention encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the appended claims.

1. A radome shell having a central axis, comprising: a first radomefabric layer wrapped in one of a clockwise or a counterclockwisedirection around the central axis within the radome shell; and a asecond radome fabric layer wrapped over the first radome fabric layer inthe other of the clockwise or the counterclockwise direction around thecentral axis within the radome shell.
 2. The radome shell of claim 1,further comprising: an organic polymer dispersed around the first radomefabric layer and second radome fabric layer.
 3. The radome shell ofclaim 1, wherein both of the first radome fabric layer and the secondradome fabric layers are e-glass.
 4. The radome shell of claim 1,wherein the radome shell is a missile radome shell, and the missileradome shell has a thickness of at least a ¼ inch.
 5. The radome shellof claim 1, further comprising: a plurality of alternating layers of thefirst radome fabric layer and the second radome fabric layer, whereineach of the plurality of first radome fabric layers are wrapped in aclockwise direction around the central axis within the radome shell, andeach of the plurality of second radome fabric layers are wrapped in acounterclockwise direction around the central axis within the radomeshell.
 6. The radome shell of claim 5, further comprising: at least onedrape fabric layer between each of the plurality of alternating layersof the first radome fabric layer and the second radome fabric layer.